The present invention relates to an improved tennis racket, and more particularly relates to an improved coupling construction of a yoke with a frame of a tennis racket suited for manufacturing by molding.
Conventional examples of the tennis racket are found in the inventions disclosed in the U.S. Pat. Nos. 3,702,701 and 3,958,805, in which the tennis racket is in general comprised of an extruded metal or molded plastic frame defining a stringing area or face and a molded plastic throat piece or yoke coupled to the frame at the shoulders of the latter.
In the following description, the sides of the elements closer to the stringing area or face will be referred to as "the inner side" whereas the opposite side of the elements will be referred to as "the outer side".
The general shape of the throat piece or yoke includes slightly concave outer side surfaces which conform in curvature to and contact the inner side surfaces of the shoulders of the frame, a concave surface defining a part of the stringing area or face of the racket and a semi-circular surface opening in the direction of the handle. The throat piece or yoke of this shape is formed separate from the frame and coupled to the shoulders of the frame by suitable fastening means such as fastening screws or adhesives. Thus, the coupling planes of the yoke is in line with the curvature of the inner side surface of the frame.
The strings are set to the frame and the yoke in a highly stretched state and the magnitude of the string tension imposed on the yoke amounts to 500 kg. or larger. Due to the above-described shape of the yoke, the converging ends of the yoke tend to shift on the shoulders of the frame in the direction of the string tension acting thereon during long use of the tennis racket, thereby causing separation of the yoke from the frame. In addition, the converging ends of the yoke tend to buckle due to the large magnitude of force applied thereto and the relatively small thickness of the portions, thereby causing early breakout of the yoke. Further, the impact force imposed on the yoke via the strings generated by hitting balls must be borne by the fastening screws or adhesives only. This stress concentration takes the form of shearing stress which causes accelerated wearing-out of the fastening screws or peeling-off of the adhesive.